1. Field of the Invention
The present invention relates to a magnetic recording member, more particularly, to a magnetic recording member with two or more magnetic layers provided on the surface of the support thereof.
2. Description of the Prior Art
Recently, in both open reel and cassette tapes the quality of magnetic recording tape has increased and an increase in the density thereof has been demanded; thus, multi-layer tapes, i.e., magnetic tapes provided with two or more magnetic layers, have been proposed.
Such magnetic tapes are described in, for example, Japanese Patent Publications No. 2218/1962, 23678/1964, Japanese Patents (Laid Open) No. 31602/1972 (U.S. Pat. No. 3,761,311), 37903/1972, 31907/1973 (U.S. Pat. No. 3,775,178), 31804/1975, U.S. Pat. Nos. 2,643,130, 2,647,954, 2,941,901, 3,676,217, German Pat. (DT-AS) Nos. 1,190,985, 1,238,072, etc.
In this case, setting of operating bias is one consideration which should be taken into account, and the set points are in the vicinity of 100%, which is generally called the standard bias. Magnetic tapes meeting these conditions are, in general, most widely used and can be used with ease, and moreover they have the advantage that no special bias setting and equalization are needed.
The most convenient method of producing magnetic tapes of high density is to increase the coercive force of the magnetic iron oxide used in the magnetic tapes. This method, however, has the disadvantage that since the magnetic tape produced by this method is not compatible with the standard bias, it is required that the user select a suitable operating bias and equalization for the magnetic tape so that the best magnetic tape characteristics be obtained, leading to confusion on the part of the user with respect to standard bias, chromium dioxide bias, and multilayer bias in selection of the correct bias and equalization. Furthermore, it is difficult to use such magnetic tapes interchangeably in various tape recorders, tape decks and the like, since such magnetic tapes require a certain bias and equalization range, which may not be found in certain tape decks. Although conventional two layer tapes have improved output in the low region, they need special operating bias and equalization positions as is shown in Table 1.
Table 1 ______________________________________ Kind of Magnetic Tape Bias (%)*.sup.1 Equalization (.mu. sec*.sup.2) ______________________________________ Low Noise Type 100 120 Fe-Cr Type*.sup.3 130 35 to 50 CrO.sub.2 Type 160 70 ______________________________________ *.sup.1 Indicated with Low Noise Type as basis (100%). *.sup.2 Indicated with time constant (.mu. sec) of equalization of Low Noise Type as the basis (120 .mu. sec). In the case of the Fe-Cr Type, it is generally 40 to 60% of the basis, and in the case of CrO.sub.2 Type, i is generally 50 to 70% of the basis based on low noise type. *.sup.3 DUAD Ferri-Chrome Tape (trade name, produced by Sony Corp.) in which the upper layer comprises CrO.sub.2 and the lower layer comprises maghemite, Scotch CLASSIC Cassette (trade name, produced by 3 M Co., Ltd.), etc., are typical.
Therefore, unless tape recorders, tape decks, and the like are provided with bias and equalization positions as shown in Table 1, it is impossible to use magnetic tapes under the best conditions. Furthermore, it is necessary to select tape recorders, tape decks, and the like depending upon magnetic tapes of various companies. In this way, the major drawback of the above magnetic tapes is their lack of interchangeability.
The present invention provides magnetic tapes which remove the above described drawbacks involved in selecting an appropriate operating bias and equalization, etc., which can be used interchangeably in conventional tape recorders, tape decks, and the like, and which have excellent properties, and thus the present invention is concerned with magnetic tapes provided with two or more magnetic layers on the surface of the support thereof.